This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
The present invention describes an acquisition strategy that is applicable to magnetic resonance imaging (MRI) to acquire multiple sections of an image data set and combine them to increase the signal to noise (SNR) compared to a comparable single acquisition of the data. The MRI signal space is termed k-space, and conventional rectilinear scanning methods acquire k-space data such that each image k-space data point is sampled only once, and all regions are sampled with uniform density. Conversely, radial/projective approaches to sampling k-space obtain data as a series of lines that traverse the center of k-space, effectively obtaining a higher density of sampled points near the center of k-space, FIG. 1. FIG. 1 shows the trajectory of sample lines of k-space are indicated for projective/radial sampling schemes. In these schemes, all lines pass through the center of k-space, leading to the highest sampling density near the center and progressively lower sampling density towards the periphery of k-space.
Recently, an approach termed Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction (PROPELLER) has been described based on sets of multiple parallel lines or “blades”, with each set of parallel lines directed parallel to a radial or diagonal line of k-space, FIG. 2. FIG. 2 shows the approach of acquiring multiple parallel lines to describe a rectangular region of k-space (blade) has previously been described for the PROPELLER imaging approach. The rectangle encompassing the individual lines indicates the region of k-space sampled in this case. “Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) MRI: Application to Motion Correction,” Pipe, Proc. Intl. Magn. Reson. Med. 7 (1999), p. 242, incorporated by reference herein.
To acquire complete k-space coverage in the PROPELLER approach, multiple sets of these rectangular sampled blades are applied to k-space such that blades are progressively rotated about the center to completely cover k-space with at least a minimum density equivalent to the sampling density of each blade, FIG. 3. FIG. 3 shows the manner in which blades of the PROPELLER imaging approach are applied to sample k-space is illustrated. Each set of rectangular sampled regions (blades) are progressively rotated about the center of k-space until some pre-defined uniform coverage sampling density is achieved. Typically this approach requires scanning more lines of k-space than are required for rectilinear scanning approaches, leading to long scan times. The primary benefit of the multiple sets of parallel lines being that the central region of k-space is repetitively sampled, allowing motion compensation approaches to be applied to each k-space blade.